The present invention relates to inductive magnetic transducers, which may for example be employed in information storage systems or measurement and testing systems.
Inductive heads used for writing and/or reading magnetic information on storage media such as a disk or tape typically include electrically conductive coil windings encircled by a magnetic core including first and second pole layers. Portions of the pole layers adjacent the media are termed pole tips. The magnetic core is interrupted by a submicron nonmagnetic gap disposed between the pole tips to divert magnetic flux to the media during writing. To write to the media electric current is flowed through the coil, which produces magnetic flux in the core encircling the coil windings, the magnetic flux fringing across the nonmagnetic gap adjacent to the media so as to write bits of magnetic field information in tracks on the media.
The first pole layer may also serve as a magnetic shield layer for a magnetoresistive (MR) sensor that has been formed prior to the pole layers, the combined MR and inductive transducers termed a merged or piggyback head. Typically the first pole layer is substantially flat and the second pole layer is curved, as a part of the second pole layer is formed over the coil windings and insulation disposed between the pole layers, while another part nearly adjoins the first pole layer adjacent the gap. The second pole layer may also diverge from a flat plane by curving to meet the first pole layer in a region distal to the media-facing surface, sometimes termed the back gap region, although typically a nonmagnetic gap in the core does not exist at this location.
The curvature of the second pole layer from planar affects the performance of the head. An important parameter of the head is the throat height, which is the distance from the media-facing surface to where the first and second pole layers begin to diverge and become separated by more than the submicron nonmagnetic gap. Because less magnetic flux crosses the gap as the pole layers are further separated, a short throat height is desirable in obtaining a fringing field for writing to the media that is a significant fraction of the total flux crossing the gap.
In addition to the second pole layer being curved from planar, one or both pole layers may also have a tapered width in the pole tip area, to funnel flux through the pole tips. A place where the second pole layer begins to widen is sometimes termed a nose or flare point. The distance to the flare point from the media-facing surface, sometimes called the nose length, also affects the magnitude of the magnetic field produced to write information on the recording medium, due to decay of the magnetic flux as it travels down the length of the narrow second pole tip. Thus, shortening the distance of the flare point from the media-facing surface would also increase the flux reaching the recording media.
Unfortunately, the aforementioned design parameters require a tradeoff in the fabrication of the second pole tip. The second pole tip should be narrow and well-defined in order to produce narrow and well-defined written tracks on the rotating disk, but the slope of the second pole layer at the end of the throat height makes photolithography difficult. The second pole layer can be formed in two pieces to better define the pole tip; a flat pole tip layer and a curved yoke layer that are connected or stitched together. This solution, however, can actually require the throat height to be extended in order to have a sufficient stitched area for flux transfer between the second pole tip and the yoke. High-resolution photolithography, such as I-line or deep ultra violet (DUV) photolithography, may be useful for reducing feature sizes but has a more limited depth of focus that may exacerbate the problem of focusing on the sloped pole layer adjacent the throat.
In addition, several methods are known to form self-aligned pole tips. In one method, an ion beam etch (IBE) or other highly anisotropic process removes a portion of the second pole layer not protected by a mask, thereby creating the second pole tip, with the etching continued to similarly remove a portion of the first pole tip not covered by the second pole tip. The width of the pole tip layers are therefore matched, and walls of the pole tips are aligned, but the problem of accurately defining the second pole tip by photolithography for a short throat height remains. Other proposals include forming an electrically conductive gap layer, so that the second pole tip can be electroplated atop the first. A second pole tip directly plated on a conductive gap layer may have increased eddy currents that counteract high-frequency operation, however, and so has not been widely employed.
High-frequency operation may also be counteracted by self-inductance of the coil that is used to drive the magnetic flux. The number of coil turns may be reduced to reduce the self-inductance, but this generally results in reduced electromotive force. Larger coil cross-sections may be employed, but at high frequencies a skin effect may arise that limits electric current to the surface of the coil cross-sections. Other coil configurations can be employed but typically involve manufacturing difficulties.